Summary of Work: The "Mechanisms of Germ Cell Death" project aims to identify the mechanisms by which germ cells are killed in the testis. We earlier showed that the architecture of the normal seminiferous tubule was required for this apoptosis, which implicates a role for cell-cell adhesions and their related signals from the Sertoli cells. This had not been demonstrated previously. Working on glycol ether-induced pachytene apoptosis, we showed that pharmaceuticals that inhibited calcium fluxes across membranes inhibited the apoptosis.Other labs have shown similar protection in thymus. However, recently, using fluorescent confocal laser microscopy, we demonstrated that such fluxes did not, in fact, occur, and we postulated alternative mechanisms (changes in membrane-related proteins or functions). Future studies will explore membrane-associated signalling events and their alteration by glycol ethers; this project is suspended temporarily pending personnel recruitment. The manuscript identifying and defining a testicular endonuclease as cyclophilin A was published. This was the first demonstration of an endonuclease in germ cells, an enzyme that helps mediate chemically-induced apoptosis. Our data are consistent with the concept that the enzyme is always present in immature germ cells, but maintained in an inactive state until activated by some as-yet-undefined stimulus (perhaps mediated through the cell membrane-associated proteins, above). In the "Inhibited Spermiation" project, we have tentatively identified, at the light microscope level, several cytoskeletal- related proteins that may be involved in inhibited sperm release. Future immunoprecipitation studies should help identify protein-protein interactions that form the adhesions between Sertoli cells and spermatids, which will in turn lead to new understandings about how these adhesions are controlled, and interrupted by toxicants.